This invention relates to coupling structures for compound drill stems and more particularly to coupling structures that transmit torque from one drill stem section to another in roof drills.
Roof drills are utilized for drilling holes in the ceiling of a coal mine or the like. The holes are drilled to install bolts that are cemented into the holes. The bolts secure plates to the mine ceiling to prevent rocks and earth from falling from the ceiling.
When drilling holes for roof support, hard cutting conditions are encountered and water is needed as a coolant to prolong the life of the drill bit. Certain conventional arrangements that inject water up through drill stems to drilling area are effective to cool bits during drilling, but are not favored by drill operators because they are showered with a slurry of water and cuttings and because the quantity of water required produces muddy conditions on the bottom of the mine.
One known roof drill has a drill bit cooled by water injected through its drill stem to a drilling area and also extracts the water and accompanying cuttings from the drilling area to prevent the drill operator from being showered. This known arrangement employs multiple concentric passages in its stem, connected to a water source to provide cooling water to the drilling area and is connected to a vacuum source to suck off the water and cuttings from the drilling area. Such multiple length steels are necessary because of drilling long holes in areas where seam height prevents use of a one piece steel. Connections between steel sections are difficult because of this requirement for two-way passage.